(1) Field of the Invention
This invention relates to an NC laser system comprising a laser beam machine and a numerical control system associated therewith, and more particularly to a numerical control (NC) laser system of this kind adapted to deliver an ON-OFF signal for ON-OFF control of a laser oscillator thereof.
(2) Description of the Related Art
When an NC laser system is operated to cut a workpiece of metal or the like by a laser beam generated thereby, the positioning of a machining head is first completed, and then a laser oscillator is turned on in a cutting mode of the system to thereby start machining of the workpiece. However, machining started after completion of positioning of the machining head takes time to cut the workpiece. Therefore, there is conventionally employed a machining method of sending a command to turn on or off the laser oscillator while holding the NC laser system in the cutting mode. According to such a laser beam machining method, the machining head is moved without waiting for completion of positioning of the machining head, which makes it possible to reduce machining time. In laser beam cutting performed by the method, an ON-OFF signal for turning on or off the laser oscillator is generated by the same block of a machining program as that containing a move command for moving the machining head, whereby the laser oscillator is turned on or off according to the ON-OFF signal.
However, in the cutting mode, acceleration/deceleration control is performed for control of the speed of servomotors, which makes an actual machining path different from a path directed by the program due to delay of movement for machining caused by the acceleration/deceleration control. Therefore, even if an ON signal is delivered together with a move command for moving the machining head, the ON signal is not necessarily delivered at an end point of movement of the machining head directed by the move command. If interpolation of a subsequent command for moving the machining head written in the following block has already been started, the ON signal is delivered at a point different from the directed end point.
Particularly, in cutting a small circle, there are cases in which in spite of directions for holding the laser oscillator in an ON state only within or on the circle, the laser oscillator continues to be in the ON state even after the machining head is outside the circle.